In radio communication systems, such as third generation (3G) wideband code division multiple access (WCDMA) based systems, using continuous transmission and reception, the compressed mode, often referred to as the slotted mode, is needed to make measurements from another frequency without a full dual receiver terminal. The compressed mode means that transmission and reception are halted for a short time period, e.g. few milliseconds, in order to perform measurements on the other frequencies. The aim is not to lose data but to compress the data transmission in the time domain. The compressed mode is needed both for inter-frequency and inter-system handovers.
By taking a specific example, 3GPP technical specification 25.215 v8.3.0 (2009-03) Chapter 6 gives further details on compressed mode regarding universal terrestrial radio access (UTRA) frequency division duplex (FDD). On command from the universal terrestrial radio access network (UTRAN), a user equipment (UE) terminal shall monitor cells on other FDD frequencies and on other modes and radio access technologies that are supported by the UE (i.e. time division duplex (TDD), global system for mobile communications (GSM), evolved UTRA). To allow the UE to perform measurements, UTRAN shall command that the UE enters in compressed mode, depending on the UE capabilities.
The UE capabilities define whether a UE requires compressed mode in order to monitor cells on other FDD frequencies and on other modes and radio access technologies. UE capabilities indicate the need for compressed mode separately for the uplink and downlink and for each mode, radio access technology and frequency band.
A UE shall support compressed mode for all cases for which the UE indicates that compressed mode is required. A UE does not need to support compressed mode for cases for which the UE indicates that compressed mode is not required. For these cases, the UE shall support an alternative means of making the measurements.
The UE shall support one single measurement purpose for one transmission gap pattern sequence. The measurement purpose of the transmission gap pattern sequence is signalled by higher layers.
The UE shall support simultaneous compressed mode pattern sequences which can be used for different measurements. The following measurement purposes can be signalled from higher layers:                FDD;        Time division duplex (TDD);        Global system for mobile communications (GSM) carrier received signal strength indicator (RSSI) measurement;        Initial BSIC identification;        Base station identification code (BSIC) re-confirmation; and        Evolved UTRA (E-UTRA).        
The UE shall support one compressed mode pattern sequence for each measurement purpose while operating in FDD mode, assuming the UE needs compressed mode to perform the respective measurement. In case the UE supports several of the measurement purposes, it shall support in parallel one compressed mode pattern sequence for each supported measurement purpose where the UE needs compressed mode to perform the measurement. The capability of the UE to operate in compressed mode in uplink and downlink is given from the UE capabilities.
3GPP TS 25.133 v8.6.0 (2009-03), Section 8.4.2.1 gives details on UE measurement capabilities when high-speed downlink shared channel (HS-DSCH) discontinuous reception is not ongoing. In CELL_FACH state, the UE shall be able to monitor up to                32 intra frequency FDD cells and        32 inter frequency cells, including                    FDD cells distributed on up to 2 additional FDD carriers and            Depending on the UE capability, TDD mode cells, distributed on up to 3 TDD carriers, and                        Depending on the UE capability, 32 GSM cells distributed on up to 32 GSM carriers.        Depending on the UE capability, the UE shall be able to monitor up to 16 intra frequency cells during idle period down link (IPDL) gaps.        
The standard specification further specifies how the measurements on different systems and modes are performed given the time allocated to that system. The requirements are based on an assumption that the time during the measurement occasions that is allocated to each of the different modes and systems shall be equally shared by the modes which the UE has capability for and that are in the monitored set signalled by the network.
Section 8.4.2.5 gives details on GSM measurements when HS-DSCH discontinuous reception is not ongoing. To support cell reselection the UE shall always perform BSIC verification in Cell_FACH state.
In CELL_FACH state when measurement occasions are provided by the UTRAN, the UE shall continuously measure GSM cells and search for new GSM cells given in the monitored set.
In section 8.4.2.1 the split of measurements between different modes and systems is defined. Every second measurement occasion scheduled for GSM measurements, as given by 8.4.2.1 shall be allocated for GSM initial BSIC identification.
The remaining measurements occasions scheduled for GSM measurements shall be used as follows. 3 occasions out of 4 shall be allocated for GSM carrier RSSI measurements and 1 out of 4 shall be allocated for GSM BSIC reconfirmation. The scheduling of measurement occasions between GSM carrier RSSI measurements and GSM BSIC re-confirmation is up to the UE.
The 3GPP standard provides some minimum requirements that must be fulfilled by a UE. But some field test conditions can require going beyond the 3GPP nominal requirements.
For instance by taking a specific example of GSM carrier measurements and BSIC re-confirmation measurements, it can be realised that these second generation (2G) measurement purposes indicated in the 3GPP standard have different timing constraints: while a GSM carrier RSSI measurement can be performed at any time, the BSIC re-confirmation must be performed at a specific time instant (frame number+quarter bit position).
So as the network defines some generic gap purpose patterns, this means that a gap purpose with BSIC re-confirmation does not always match with the BSIC re-confirmation of one UE and so the BSIC re-confirmation is delayed and can lead to a loss of synchronisation with a 2G cell.
It is thus the object of the present invention to overcome the above-identified difficulties and disadvantages by proposing an improved solution for performing radio measurements.